The present invention concerns, in a first aspect, a method for compensating optical aberrations in a telescope, and more particularly, a method that comprises carrying out said compensation of optical aberrations by moving, in a controlled manner, an image acquisition device.
A second aspect of the invention concerns a system capable of implementing the method proposed by the first aspect.
There are systems applied to different classes of telescopes, both professional and amateur, for compensating different kinds of aberrations, in some cases caused by mechanical flexures, and in others by different types of optical aberrations, in general low-order aberrations.
To date, some systems used by professional astronomical observatories have been adapted and democratized for smaller, amateur-type telescopes. The following are some examples of said adaptations:
“Bisque software”: proposes the implementation of a “tpoint” model in the interface of its control systems via the “thesky” software. The “tpoint” allows modeling the aberrations of mechanical flexures and correct the position of the mount by means of an “offset”, depending on the previous result. This system allows modeling and correcting the pointing of the telescope without taking into account or correcting the optical aberrations included by the flexure of the telescope. It also fails to allow adjusting or acting on the optical alignment of the telescope.
“Maxim”: proposes a system similar to the “bisque software” based on more simplified equations, but also limited to mechanical modeling only.
“Meade”: in its more advanced telescope models it proposes an electronic collimation system that allows moving one of the mirrors along two axes to ensure the alignment in the center of the sensor. This function does not ensure the correct centering or the correct alignment of the optics in the entire sensor.
At a professional level, there are large-scale aberration compensation systems that are very complex due to the size of the instruments wherein they must be applied.
This is the case of the “Magellan” telescopes (6 m in diameter), wherein there is a positioning system to position the secondary mirror of the telescope, composed by four supporting points, which requires the use of eight actuators, implying a complex mechanical design that is undesirable to be extrapolated to the design of smaller telescopes (for example, 50 cm to 1 m in diameter).
The majority of large telescopes correct optical alignment aberrations by means of what is known as “wavefront sensing” with the use, in general, of a “Shack Hartmann” sensor. The foregoing allows correcting several optical modes, where the correction is carried out by means of actuators below the mirror but involves having a costly system, which is not of interest to be implemented in small telescopes due to the loss of light energy entailed by an additional sensor in a telescope with a small diameter.
Different patent documents describing more or less complex optical aberration compensation proposals in telescopes are cited below.
Application EP0252034A2 describes a method for correcting, through electronic means, the curvature defects in the captured images, which is applicable to mirror telescopes with large diameters. The method is based on the adjustment of the curvature of the primary mirror, which is partially elastic, by means of the adjustment of the pressure of a gas in contact with one of its faces, under the control of an electronic system in collaboration with temperature and pressure-detecting devices, and optionally, with monitoring laser systems of the curvature of the primary mirror.
Patent EP1208402B1 proposes a semi-active thermal compensation and focusing system of a three-mirror anastigmat reflective telescope, centrally obscured, where the secondary mirror is mounted on a structure formed by thermally deformable support struts. The system comprises a series of temperature sensors arranged in the support struts, and optionally in the secondary mirror, and is envisaged for, depending on the detected temperatures, controlling the heating elements to selectively heat the struts to control the position of the secondary mirror in relation to the primary mirror, and optionally, also to control the secondary mirror to modify its curvature. This way, the relative curvatures between the secondary and primary mirrors, as well as the separation between them, are kept substantially constant, with the purpose of maintaining the telescope correctly focused.
EP1208402B1 does not indicate the possibility of controlling the position of an optical element other than the aforementioned secondary mirror, or of correcting any other type of aberrations other than those relative to defocus.
The following two records contemplate the possibility of analyzing the images acquired by an image acquisition device to detect optical aberrations and act on a mobile optical element of the telescope, with the purpose of correcting said optical aberrations.
International application WO2006127986 describes an apparatus and methods for the focusing and collimation of telescopes by means of an electronic control unit which, depending on the information referring to the optical elements, or other types of elements, of the telescope, referring to a user or a scanning or image acquisition device, controls, in general, a lens of the telescope, adjusting its position with the purpose of correcting the focus and/or collimation of the telescope.
According to an embodiment example of WO2006127986, the information on which the aforementioned control unit is based is the information included in an image captured by a camera, which is processed to determine whether the telescope is focused or collimated correctly, and to determine the appropriate adjustments relative to the orientation and/or position of the secondary mirror of the telescope to compensate the possible focus and collimation errors by acting on said secondary mirror.
WO2006127986 does not indicate or suggest acting on elements of the telescope other than the lens or the aforementioned secondary mirror, or correcting aberrations other than those relative to defocus and collimation.
U.S. Pat. No. 7,130,127B2 proposes a terrestrial telescope with a digital camera that includes a group of mobile focus lenses according to an optical axis and an image acquisition device arranged to receive the light traversing said lenses and a light reflection/transmission element arranged between both of them.
An embodiment example of U.S. Pat. No. 7,130,127B2 proposes processing the images acquired by the image acquisition device with several purposes, including correcting the generated focus and applying the corresponding control signals to the group of mobile lenses to move them along the aforementioned optical axis.
U.S. Pat. No. 7,130,127B2 also fails to indicate the possibility of correcting the position of an optical element other than the aforementioned group of lenses or correcting aberrations other than the aberrations relative to defocus.
It seems that it is necessary to offer an alternative to the state of the art that fills the gaps found therein, in particular those referring to the absence of proposals related to the compensation of optical aberrations by means of the displacement of an image acquisition device of a telescope, which may be used to detect said optical aberrations as well.